The invention pertains to a process for detecting the bit rates, in particular high bit rates, of serial data streams of data terminals, the control commands of the stream beginning with uniform binary characters.
The data transmission devices according to the state of the art such as modems with the standardized AT command set, which is a standard command language for communicating with data transmission devices, usually make it possible for data to be transmitted to and from the data terminal at various transmission speeds.
Problems occur when the data transmission device must be able to detect the transmission rate used by the data terminal so that it can adjust itself to that rate. Detection is possible in principle because all the control commands from the data terminal to the data transmission device begin with uniform binary characters such as, for example, the ASCII symbol "A" (=binary 01000001) or "a" (=binary 01100001).
In a known process for detecting the bit rate, the received data stream is sampled at a multiple of the maximum bit rate to be expected and compared in software with various bit patterns. Once the bit pattern has been determined, it is then possible to make a conclusion concerning the bit rate and the binary characters received ("A" or "a"). In the known process, the entire command line must be evaluated, that is, processed in software bit for bit.
This process suffers from the disadvantages that it can be realized only for low bit rates and only with the simultaneous help of a significant amount of the processing power of the CPU present in the data transmission device. Under favorable conditions, therefore, it is possible to deal with bit rates of only up to 57,600 bits/second.